The prior art has recognized the potential of peat moss material for use as an absorbent medium in structures for absorbing aqueous solutions. The remarkable fluid absorption properties of peat moss material have been turned to use in the field of sanitary, disposable absorbent products such as sanitary napkins, tampons, diapers, adult briefs, urinary pads, wound dressings and the like, to provide highly efficient absorbent components which can be made relatively thin for better fit, comfort and discretion, while being sufficiently absorbent to prevent overflow leakage of body exudate and garment staining.
The following United States patents document the use of peat moss material for manufacturing absorbent components for sanitary, disposable absorbent products.
______________________________________ U.S. Pat. No. INVENTOR(s) DATE Of ISSUE ______________________________________ 4,170,515 Lalancette et al. October 9, 1979 4,215,692 Levesque August 5, 1980 4,226,237 Levesque October 7, 1980 4,305,393 Nguyen December 15, 1981 4,473,440 Ovans September 25, 1984 4,507,122 Levesque March 26, 1985 4,618,496 Brasseur October 21, 1986 4,676,871 Cadieux et al. June 30, 1987 4,992,324 Dube February 12, 1991 5,053,029 Yang October 1, 1991 ______________________________________
The subject matter of these patents is incorporated herein by reference.
Peat moss material can be formed in a highly cohesive, structurally integral board by any one of the methods disclosed in the above-identified prior art. In board form, the absorbent material is more convenient to handle and it can be directly processed in high speed automatic equipment for assembling disposable absorbent products.
Broadly stated, the method developed by the industry for manufacturing a structurally integral peat moss board which is specifically adapted for sanitary usage, comprises the following steps. Raw peat moss, in particulate form, is classified by wet screening in order to retain only the particles which are the most absorbent. The screened fraction is diluted with water to form a slurry having a pumpable consistency which is sheeted on a Fourdrinier wire and dewatered by the sequential application of vacuum and heat. The thus formed board is calendered at high pressure to increase its density primarily for the purpose of enhancing its drying power, i.e. the ability of the absorbent medium to continuously pull and wick fluid away from adjacent materials such that virtually all the fluid is collected in the peat moss core. This consideration is particularly important for sanitary absorbent products which are intended to remain in contact with the skin of the wearer for an appreciable period of time. In such applications, the capability of the peat moss core to extract moisture from the fluid permeable cover of the sanitary product which receives the discharge of body exudate is a highly desirable attribute as it allows to impart to the fluid permeable cover a feeling of "dryness" which makes the absorbent product more comfortable to wear.
During the formation stage of the peat moss board, the aqueous slurry is treated with a wetting agent (hereinafter "wetting agent" shall be construed to encompass any substance which imparts hydrophilicity or enhances the hydrophilicity of the peat moss material), such as a surfactant, to provide the peat moss board with a strong affinity for water. Typically, the wetting agent is added to the peat moss slurry at the vacuum dewatering stage by spraying or by any other appropriate deposition method. The pressure differential established across the Fourdrinier wire to extract dilution water constitutes the agency which causes the wetting agent to penetrate deeply in the peat moss slurry.
The prior art also recognizes the efficiency of peat moss material to absorb non-aqueous liquids such as a variety of chemical products and specifically oil-based materials. The waste management industry has been using peat moss as an absorbent medium for the removal of non-aqueous, liquid pollutants, for many years. Typically, dried particulate peat moss packaged into liquid permeable pouches is delivered to the contaminated area and placed in contact with the liquid spill to absorb the pollutant. By virtue of the relatively low density of peat moss material in particulate form, the absorbent pads have the ability to float on water and can be used for recovering non-aqueous, liquid pollutants floating on a body of water, such as an oil slick on sea surface for example.
Although particulate peat moss material has the ability to collect and trap many times its own weight of oil-based products and a variety of other chemicals, the configuration of the absorbent pads made from this material is not well suited for the recovery of large scale spills. Granular peat moss material has virtually no structural integrity, and when it is loaded into a flexible containment pouch, the resulting absorbent pad assumes the shape of a bag, i.e. a bulbous round body in which the ratio outer surface/volume is relatively low. As a result, the liquid take-up rate is low which requires a longer residence time of the absorbent pad in the spill in order to reach the saturation level. This drawback is particularly significant for applications where the absorbent pad is subjected in use to vigorous movements by natural forces, such as sea waves or wind, having a tendency to separate the absorbent pad from the spill. In such applications a high fluid take-up rate is highly desirable to allow an efficient utilization of the available absorbent material.
Having regard to the foregoing, a primary objective when designing an absorbent pad for spill management purposes should be to attain the broadest possible outer surface in order to increase the contact surface with the liquid pollutant and therefore to enhance the liquid take-up rate. A suitable shape would be a sheet-like or a board-like configuration which is characterized by a broad outer surface and little thickness.
However, granular peat moss material which is currently used by the industry is unsuitable for making board-shaped absorbent pads because it has little or no ability to maintain a predetermined shape, unless one uses a liquid permeable pouch which cumulates the functions of a containment envelope and of a structural member to impart to the absorbent material a certain shape. However, for cost-considerations, this option is unpractical.
To compensate for the limited outer surface of conventional absorbent pads, one may use a larger number of pads for a given amount of liquid pollutant. The drawback behind this approach is twofold. Firstly, a larger number of absorbent pads makes the recovery operation more expensive. Secondly, this practice, in itself, may create an environmental hazard because the pouches used to contain the loose peat moss material are made from a non-biodegradable plastic such as a non-woven polyester fabric, therefore if some absorbent pads drift away during the recovery operation and are lost they will contaminate the environment.
It has also been suggested in the past to apply peat moss material to the liquid pollutant in particulate form and subsequently to recover the peat moss material with the liquid pollutant trapped therein. This method avoids the difficulties associated with absorbent pads made of granular peat moss material packaged in liquid permeable pouches, however, this use is restricted only to land or hard surfaces and on spills of limited extend. Loose peat moss material cannot be practically used for large-scale spills on land or on water because the recovery of the spent absorbent is strenuous and costly due to its particulate nature.